The Yahoo Query Language is an expressive SQL-like language that lets you query, filter, and join data across Web services. With YQL, apps run faster with fewer lines of code and a smaller network footprint

A window function performs a calculation across a set of table rows that are somehow related to the current row. This is comparable to the type of calculation that can be done with an aggregate function. But unlike regular aggregate functions, use of a window function does not cause rows to become grouped into a single output row — the rows retain their separate identities. Behind the scenes, the window function is able to access more than just the current row of the query result.